Wells in compactable sediments (or tectonically active areas) are subject to deformation over the productive life of the field. The result is the catastrophic loss of producing zones up to and including the loss of a whole well. The problem is exacerbated by the increasingly rapid off-take rates and the completion of multiple zones in a single well. The observable phenomenon is that at first a well casing will bend or begin to buckle, frequently at casing joints, or interfaces in the formation. As the compaction continues, the movement results in a significant misalignment of the well axis. The result can be the complete loss of the well investment resulting in deferred and/or lost production, if not the replacement cost of a well, which is extremely expensive. The ability to detect early bending would warn of a later buckle or collapse and allow for changes in production practices and/or remedial action. Detection of deformation forces, in-situ, can become a complex problem, particularly when such forces include axial, hoop and shear stresses.
U.S. Pat. No. 6,854,327, incorporated herein by reference, describes the use of bent, instead of stretched, FBG sensors that alter amplitude reflection and broaden frequency. The FBG sensors react to displacement forces with a predictable, altered, wavelength response that may be compared with a calibration curve to estimate shape and the magnitude of displacement. One embodiment is described as a helical-shaped optical fiber, wherein the FBG sensors are positioned in the bends of the optical fiber.
A need exists for an improved method of applying strain sensors to a cylindrical object for detecting and/or imaging and/or measuring deformations of the object.